Perpendicular magnetic tunnel junction (pMTJ) with in-plane magneto-static switching-enhancing layer

ABSTRACT

An STTMRAM element includes a magnetic tunnel junction (MTJ) having a perpendicular magnetic orientation. The MTJ includes a barrier layer, a free layer formed on top of the barrier layer and having a magnetic orientation that is perpendicular and switchable relative to the magnetic orientation of the fixed layer. The magnetic orientation of the free layer switches when electrical current flows through the STTMRAM element. A switching-enhancing layer (SEL), separated from the free layer by a spacer layer, is formed on top of the free layer and has an in-plane magnetic orientation and generates magneto-static fields onto the free layer, causing the magnetic moments of the outer edges of the free layer to tilt with an in-plane component while minimally disturbing the magnetic moment at the center of the free layer to ease the switching of the free layer and to reduce the threshold voltage/current.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a reissue application of U.S. Pat. No.9,679,625, issued from U.S. patent application Ser. No. 14/930,523,which is a continuation of the commonly assigned application bearingSer. No. 13/161,412 filed on Jun. 15, 2011, entitled “PERPENDICULARMAGNETIC TUNNEL JUNCTION (pMTJ) WITH IN-PLANE MAGNETO-STATICSWITCHING-ENHANCING LAYER,” which is a continuation-in-part of apreviously-filed continuation-in-part (CIP) U.S. patent application Ser.No. 13/099,321, filed on May 2, 2011, by Zhou et al. and entitled“Magnetic Random Access Memory With Field Compensation Layer andMulti-Level Cell”, which is a CIP of U.S. patent application Ser. No.13/029,054, filed on Feb. 16, 2011, by Zhou et al. and entitled“Magnetic Random Access Memory With Field Compensation Layer andMulti-Level Cell”.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates generally to a magnetic memory elementhaving a magnetic tunnel junctions (MTJ) and particularly to a magneticmemory element having an MTJ with perpendicular anisotropy.

Background

Magnetic random access memory (MRAM) is rapidly gaining popularity asits use in replacing conventional memory is showing promise. Magnetictunnel junctions (MTJs), an essential part of the MRAM, used to storeinformation, are made of various layers, at least some of whichdetermine the magnetic characteristic of the MRAM. An exemplary MTJ usesspin transfer torque to effectuate a change in the direction ofmagnetization of one or more free layers in the MTJ. That is, writing abit (“1” or “0” in digital logic) of information is achieved by using aspin polarized current flowing through the MTJ, instead of using amagnetic field, to change states or program/write/erase the MRAM.

In spin transfer torque (STT) MTJ designs, when electrons flow acrossthe MTJ stack, which is commonly referred to as “MTJ”, in a directionthat is perpendicular to the film plane or from the pinned (sometimesreferred to as “reference” or “fixed”) layer to the free (sometimesreferred to as “switching” or “storage”) layer, spin torque fromelectrons transmitted from the pinned layer to the free layer orientatesthe free layer magnetization in a direction that is parallel to that ofthe reference (or pinned) layer. When electrons flow from the free layerto the pinned layer, spin torque from electrons that are reflected fromthe pinned layer back into the free layer orientates the free layermagnetization to be anti-parallel relative to the magnetization of thepinned layer. Thus, controlling the electron (current) flow directioncauses switching of the direction of magnetization of the free layer.Resistance across the MTJ stack changes between low and high statesbased on the magnetization of the free layer, i.e. parallel versusanti-parallel, relative to that of the pinned layer.

However, a problem consistently experienced and preventing advancementof the use of MTJs in STTMRAM designs is reducing the threshold voltageor current used to switch the free layer magnetization during writeoperations. Such current and threshold voltage requirements limit theuse of spin transfer torque-based MTJ devices in practical applications.

MTJs with perpendicular anisotropy, such that the magnetic moments ofthe free layer and the fixed layer thereof are in perpendiculardirections relative to the plane of the film, are more appealing thantheir in-plane anisotropy counterparts largely due to the density andthermal stability improvements realized by the former.

While attempts are made to reduce the switching current and voltage ofthe MTJ, such attempts have largely addressed in-plane MTJ designs andnot perpendicular MTJs. One way to reduce the switching current andvoltage is to ease the switching of the free layer of an MTJ. Existingperpendicular MTJ designs include a free layer whose magneticorientation (also referred to as anisotropy) relative to a reference(“fixed”) layer, while perpendicular in direction, has high effectivecoercivity field (Hc). Effective Hc throughout the free layer isnon-uniform. That is, effective perpendicular coercivity field (Hc) ofthe free layer changes relative to the position within the free layersuch that the center of the free layer generally has a lower effectiveHc than the outer edges of the free layer with effective Hc essentiallyincreasing from the center of the free layer to its outer edges.

Lower effective Hc of the free layer would allow easier switching of thefree layer and would lower the threshold voltage and current required toswitch the magnetization of the free layer.

Thus, the need arises for decreasing the overall effective perpendicularanisotropic field of the free layer of magnetic memory element andthereby reducing the threshold voltage and current required to operatethe same, with minimal impact on thermal stability of the free layer.

SUMMARY OF THE INVENTION

Briefly, a spin transfer torque magnetic random access memory (STTMRAM)element has a perpendicular magnetic orientation and is configured tostore a state when electrical current is applied thereto. The STTMRAMelement includes a seed layer, a magnetic tunnel junction (MTJ) with aperpendicular magnetic orientation including, a pinned layer withanti-ferromagnetic (AFM) layer formed on top of the seed layer andhaving a fixed perpendicular magnetic orientation, a barrier layerformed on top of the pinned layer, and a free layer formed on top of thebarrier layer. The free layer has a magnetic orientation that isperpendicular and switchable relative to the magnetic orientation of thefixed layer. The magnetic orientation of the free layer switches whenelectrical current flows through the STTMRAM element. Aswitching-enhancing layer (SEL) is formed on top of the MTJ. The SEL hasan in-plane magnetic orientation and generates magneto-static fieldsonto the free layer, causing the magnetic moments of the outer edges ofthe free layer to tilt with an in-plane component while minimallydisturbing the magnetic moment at the center of the free layer to easethe switching of the free layer and to reduce the thresholdvoltage/current.

These and other objects and advantages of the present invention will nodoubt become apparent to those skilled in the art after having read thefollowing detailed description of the various embodiments illustrated inthe several figures of the drawing.

IN THE DRAWINGS

FIG. 1 shows the relevant portion of a spin transfer torque magneticrandom access memory (STTMRAM) element 10, in accordance with anembodiment of the present invention.

FIG. 2 shows the relevant portion of an STTMRAM element 30, inaccordance with another embodiment of the present invention.

FIG. 3 shows the STTMRAM element 10 when current is applied withelectrons flowing from the BL 12 to the cap layer 28 and the element 10is switching states from anti-parallel to parallel.

FIG. 4 shows the element 10 experiencing the application of electronflow, shown in a direction by the arrows 31, to be applied at the caplayer 28, flowing through the rest of the element 10, to the BL 12.

FIG. 5 shows a graph 50 of the characteristics of the elements 10 and 30having different thicknesses vs. prior art magnetic elements.

FIG. 6 shows a graph 60 of the characteristics of the elements 10 and 30having different Hk vs. prior art magnetic elements.

FIG. 7 shows the element 10 to include various embodiments of the SEL26.

FIG. 8 shows the element 10 to include still further embodiments of theSEL 26.

FIG. 9 shows the element 10 to include various embodiments of the layer24.

FIG. 10 shows the relevant portion of an STTMRAM element 120 inaccordance with another embodiment of the present invention.

FIG. 11 shows a graph 170 of the behavior of the element 120 vs. that ofa prior art magnetic memory.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following description of the embodiments, reference is made tothe accompanying drawings that form a part hereof, and in which is shownby way of illustration of the specific embodiments in which theinvention may be practiced. It is to be understood that otherembodiments may be utilized because structural changes may be madewithout departing from the scope of the present invention. It should benoted that the figures discussed herein are not drawn to scale andthicknesses of lines are not indicative of actual sizes.

In an embodiment of the present invention, a spin transfer torquemagnetic random access memory (STTMRAM) element and a method ofmanufacturing the same is disclosed. The STTMRAM element has asubstantially perpendicular magnetic orientation and is configured toprogram (or write) a state. Relevant layers of the STTMRAM elementinclude a seed layer and a magnetic (also referred to as “magneto”)tunnel junction (MTJ) having a perpendicular magnetic anisotropy. TheMTJ includes a pinned layer with anti-ferromagnetic (AFM) layer, whichis formed on top of the seed layer, with a perpendicular fixed magneticorientation. The MTJ further includes a barrier layer formed on top ofthe pinned layer and a free layer formed on top of the barrier layerwith the free layer having a magnetic orientation that is substantiallyperpendicular relative to the film plane and switchable relative to themagnetic orientation of the fixed layer. The magnetic orientation of thefree layer switches when electrical current flows through the STTMRAMelement. The free layer, by itself, has a magnetic moment in a directionsubstantially perpendicular relative to the substrate at its center, andfurther has magnetic moments at its outer edges that are alsosubstantially perpendicular relative to the substrate in their magneticdirections. A switching-enhancing layer (SEL), along with a spacerlayer, is formed on top of the free layer and has an in-plane magneticorientation. The SEL generates magneto-static fields affecting the outeredges of the free layer, causing the magnetization (or “magneticorientation”) of the free layer at its outer edges to have an in-planecomponent but minimally disturbing the magnetization at the center ofthe free layer. That is, magnetization at the outer edges of the freelayer tilts with an in-plane component, caused by the magneto-staticfield from the SEL, thereby resulting in stronger spin torque at theouter edges to initiate the magnetization switching at the outer edgesof the free layer. Moreover, through intra-layer exchange coupling,magnetization switching at the outer edges propagates to the center ofthe free layer and starts the switching of the magnetization at thecenter of the free layer. The latter is in addition to the switching ofmagnetization at the center of the free layer owing to the spin torqueassociated therewith. This advantageously results in easier switching ofthe free layer with a free layer edge magnetic moment that is tiltedwith in-plane component rather than a magnetic moment that is completelyperpendicular.

FIG. 1 shows the relevant portion of a spin transfer torque magneticrandom access memory (STTMRAM) element 10, in accordance with anembodiment of the present invention. The STTMRAM element 10 is shown toinclude a bottom electrode (BE) 12 on top of which is shown formed aseed layer 14, on top of which is shown formed an anti-ferromagneticlayer 16, on top of which is shown formed a pinned layer (PL) 18, on topof which is shown formed a barrier layer 20, on top of which is shownformed a free layer (FL) 22, on top of which is shown formed a spacerlayer 24, on top of which is shown formed a switching-enhancing layer26, on top of which is shown formed a cap layer 28. It is noted that thelayer 28 also serves as the top electrode, readily known to those in thefield.

It is noted that the pinned layer 18 is sometimes referred to as a“fixed layer” and the barrier layer 20 is sometimes referred to as a“tunnel layer” or a “barrier tunnel layer” or a “tunnel barrier layer”and the free layer 22 is sometimes referred to as a “switching layer” or“memory layer” or “storage layer” and the spacer layer 24 is sometimesreferred to as a “separator layer” and the cap layer 28 is sometimesreferred to as a “capping layer”. It is understood that other layers,not shown in FIG. 1, may be and are typically formed on top of the layer28, below the layer 12 and/or in between any of the layers shown inFIG. 1. It is also understood that the same applies to alternativeembodiments shown and discussed herein relative to subsequent figures.It is further understood that the BE 12 is formed on top of a substrateand semiconductor device layers not shown in FIG. 1 but well known tothose in the art.

The layer 18 is shown to have a magnetic moment (also known as“magnetization”) in a direction shown by the arrow 19, the layer 22 isshown to have a magnetic moment in a direction shown by the arrow 21 andthe layer 26 is shown to have a magnetic moment in a direction shown bythe arrow 23. Electrons flow into the element 10, either at 31 or at 33,during read and write operations. It is noted that electrical current isapplied to the element 10, during a write operation, at 31 and 33 but ina direction that is opposite to the direction of electron flow. Theelement 10 is generally used to store digital information (or data)during write or program operations and this information is read duringread operations. For these operations, various devices are coupled tothe element 10 that are not shown in FIG. 1, such as an accesstransistor, known to those in the art. For a description of thesedevices and methods of reading from and writing to the element 10, thereader is directed to U.S. patent application Ser. No. 11/674,124, filedon Feb. 12, 2007, by Rajiv Yadav Ranjan, and entitled “Non-UniformSwitching Based Non-Volatile Magnetic Based Memory”, the disclosures ofwhich are incorporated herein by reference.

The element 10 has a perpendicular anisotropy in that the layer 22 has amagnetic moment that is perpendicular relative to the film plane.Similarly, the layer 18 has such a perpendicular anisotropy. The element10 switches states to store a digital value in correspondence with themagnetic orientation of the layer 22 in that when this orientation isparallel to the magnetic orientation of the layer 18, the element 10 isin one state (“0” or “1”), generally referred to as “parallel”, and whenthe orientation of the layer 22 is anti-parallel, relative to theorientation of the layer 18, the element 10 is in an opposite state.These different states result in unique resistances across the element10. In this manner, the digital value of “1” or “0” is distinguishedduring read operations.

In some embodiments, the BE 12 is made of tantalum (Ta), tantalumnitride (TaN), titanium nitride (TiN), ruthenium (Ru) or copper (Cu),the layer 14 is made of one or more elements from tantalum (Ta),titanium (Ti), niobium (Nb), nickel (Ni), molybdenum (Mo), vanadium (V),tungsten (W), silicon (Si), copper (Cu), aluminum (Al) chromium (Cr),Ru, or multilayers made of any combination of these materials. The layer16 is made of platinum manganese (PtMn), iron manganese (FeMn), oriridium manganese (IrMn), and the layer 18 is made of Co, iron or Ni oran alloy made from a combination thereof or from Co, Fe, Ni or X or anycombination thereof and where X is one or a combination of non-magneticelements such as chromium (Cr), platinum (Pt), tantalum (Ta), titanium(Ti), tungsten (W), boron (B), vanadium (V), niobium (Nb), nickel (Ni),molybdenum (Mo), tungsten (W), silicon (Si), copper (Cu), aluminum (Al),gallium (Ga), platinum (Pt), palladium (Pd), samarium (Sm), oxygen (O),and nitrogen (N). Similarly, the layer 22 is made of a materialtypically used by the industry for making a free layer, as is the layer20 made of a material known for making a tunnel layer.

It should be noted that while the embodiments of FIGS. 1 and 2 each showan AFM layer adjacent to the pinned layer, in certain embodiments thislayer may not be present. In such case, one or more seed layers may beintroduced in place of the AFM layer 16 to facilitate better crystalgrowth of the pinned layer, leading to a higher anisotropy.

While the layers 22 and 18 are each shown to be made of a single layer,in alternate embodiments, each of these layers may be made of multiplelayers or one layer can be made of a single layer and the other can bemade of multiple layers. Additionally and still alternatively, each ofthe layers 22 and 18 may be made of synthetic anti-ferromagneticmaterials. Additionally, it should be noted that a thin layer of CoFeB,typically less than 2 nm thick, is introduced on either side of thebarrier layer 20, and between layers 20 and 22, and layers 20 and 18 toenhance the spin polarization, leading to a higher TMR. In oneembodiment, about 1 nm thick Co₂₀Fe₆₀B₂₀ was introduced on either sideof the barrier layer 20.

The layer 24 is a non-magnetic layer and is advantageouslynon-spin-depolarizing, which causes the element 10 to be set apart fromprior art MRAM structures because in the latter case, even when using aspacer layer, this layer has to be non-spin-depolarizing.Non-spin-depolarizing refers to electron spin not being disturbed orflipped when passing through the layer. Additionally, the element 10 isset apart from prior art in-plane MRAM structures with spin polarizerdue to its perpendicular anisotropy.

The layers 16, 18, 20 and 22 define the MTJ of the element 10 and due tothe magnetization orientation of the FL 22 and the PL 18, the MTJ of theelement 10 is considered to be a perpendicular MTJ (pMTJ).

As will be shown in greater detail shortly and discussed further, theSEL 26 advantageously causes the switching (also referred to herein asthe “threshold”) current/voltage required to program the element 10 toalso be reduced. In some cases, such a decrease is 20-25% or more overprior art structures that do not use the SEL 26. As shown by the arrow23, the direction of magnetization of the SEL 26 is in-plane and notperpendicular, this is important in the influence the SEL 26 has on theFL 22 relative to reducing the overall effective Hc of the FL 22, whichcontributes to the reduction of the current and voltage required toswitch the element 10.

The structure of the element 10 is considered to be a “bottom structure”because the FL 22 is shown formed on top of the PL 18. In the case wherean STTMRAM element has a top structure, the free layer thereof is formedbelow its pinned layer, as shown in FIG. 2.

FIG. 2 shows the relevant portion of an STTMRAM element 30, inaccordance with another embodiment of the present invention. The element30 is analogous to the element 10 except that it has a “top structure”with the pinned layer 18 formed on top of the free layer 22. Similarly,some of the other layers are positioned differently in that the seedlayer 14 is shown formed on top of the BE 12, the SEL 26 is shown formedon top of the seed layer 14, the spacer layer 24 is shown formed on topof the SEL 26, the FL 22 is shown formed on top of the spacer layer 24,the barrier layer 20 is shown formed on top of the FL 22, the PL 18 isshown formed on top of the barrier layer 20, the AFM layer 16 is shownformed on top of the PL 18 and the cap layer 28 is shown formed on topof the AFM layer 16.

FIG. 3 shows the STTMRAM element 10 when current is applied withelectrons flowing from the BE 12 to the cap layer 28 and the element 10is switching states from anti-parallel to parallel. The SEL 26 is shownto generate magneto-static field, shown by the arrows 40 and 42, onmostly the edges of the FL 22 causing tilting of the magnetization withan in-plane component at the outer edges of the FL 22 yet resulting inminimal disturbance of the magnetization at the center of the FL 22. Themagnetization at the edges of the FL 22 are shown by the arrows 44 andare substantially in a direction that is out-of-plane with smallin-plane component while the magnetization at substantially the centerof the free layer, shown by the arrow 46, is perpendicular relative tothe plane of the film. It is noted that the longitudinal demagnetizationfield from the SEL 26 is stronger at the edges of the FL 22 and decaysat the center of the FL 22 as shown by the dashed line 48 in FIG. 3. Inthis respect, while the magnetization at the outer edges of the FL 22 istilted in the presence of the SEL 26, the magnetization at the center ofthe FL 22 is less affected and remains substantially perpendicular. InFIG. 3, the SEL 26 is shown to have a positive magnetic charge 36 on itsleft side, indicated by the symbol “+”, and a negative magnetic charge38 on its right side, indicate by the symbol “−”.

In some embodiments, the SEL 26 has a thickness of 1 nm to 10 nm.

With the electron flow shown by the arrow 33, the majority of theelectrons with spin polarized by the pinned layer are transmittedthrough the barrier to the free layer. Spin momentum exerts larger spintorque at the outer edges of the FL 22 to assist switching.Advantageously, in operation, the magnetic moment, shown by the arrow 44is tilted with an in-plane component having a large torque contributingto switching and the magnetization 46, at the center of the FL 22,switches following edge switching through the intra-layer exchangecoupling thereof. The SEL 26 causes easing of the switching of the FL 22by providing an in-plane biasing field at the outer edges of the FL 22,which effectively reduces the required switching current.

FIG. 4 shows the element 10 experiencing the application of switching orelectrical current with electron flow, shown in a direction by thearrows 31, to be applied at the cap layer 28, flowing through the restof the element 10, to the BE 12. In the embodiment of FIG. 4, theelement 10 switches from a parallel state to an anti-parallel state. Theelectrons with a spin not aligned with the pinned layer areback-scattered to reverse the free layer magnetic orientation.

FIG. 5 shows a graph 50 including a y-axis representing the resistance,in kilo ohms, of the MTJ of various STTMRAM elements and an x-axisrepresenting the voltage, in milli volts, applied to the STTMRAMelements. The voltage in the x-axis is the voltage referred to herein asthe “threshold voltage” and it is the voltage at which the STTMRAMelement changes resistance. The curve 52 shows the simulated performanceof a conventional pMTJ element with no SEL while the curve 54 shows thesimulated performance of the element 10 and the element 30 where the SEL26 is 3 nano meters in thickness and the magnetic anisotropy, Hk,thereof is 5 kOe. As shown in FIG. 5, there is somewhere between a20-25% reduction in the voltage (and current) required to switch each ofthe elements 10 and 30 than that of a counterpart prior art element.

The curve 56 shows the performance of the elements 10 and 30 where theSEL 26 is 5 nano meters in thickness and as shown, the thicker SELyields more voltage reduction. For example, a 20 milli volt reduction isshown by the curve 56. It is noted that generally, the thicker the SEL26, the more effective the current reduction realized but the morechallenge in forming the MTJ due to the etching process involved.

FIG. 6 shows a graph 60 of the characteristics of the elements 10 and 30vs. prior art magnetic elements. In FIG. 6, the x-axis represents thethreshold voltage, in milli volts, applied to the magnetic elements andthe y-axis represents the MTJ resistance, in kilo Ohms, of the magneticelements.

The curve 62 shows the behavior of a prior art magnetic element, whereasthe curve 64 shows the behavior of the element 10 where the thickness ofthe SEL 26 is 5 nano meters and the Hk is 1 kOe. The curve 66 shows thebehavior of the element 10 with the SEL 26 having a thickness of 5 nanometers and an Hk of 5 kOe. Again, there is a substantial reduction ofthreshold voltage/current experienced when the SEL 26 is employed overprior art magnetic memory. Additionally, the threshold voltage increasesby 20 milli volts when the Hk is reduced from 5 kOe to 1 kOe. That isbecause a weakly-pinned SEL is another damping source for the FL 22 whenit is switching. It is recommended that an Hk of 1 kOe or larger is aneffective magnetic anisotropy required for the SEL 26.

FIG. 7 shows the elements 10 and 30 to include various embodiments ofthe SEL 26. In one embodiment, the SEL 26 is made of single layer 72ferromagnetic (FM) material and has an in-plane anisotropy, as shown bythe arrow 84. In this respect, in some embodiments, the SEL 26 is madeof cobalt (Co), iron or nickel (Ni) or an alloy made from a combinationthereof or from Co, Fe, Ni or X or any combination thereof and where Xis one or a combination of non-magnetic elements such as chromium (Cr),platinum (Pt), tantalum (Ta), titanium (Ti), tungsten (W), boron (B),vanadium (V), niobium (Nb), nickel (Ni), molybdenum (Mo), tungsten (W),silicon (Si), copper (Cu), aluminum (Al), gallium (Ga), platinum (Pt),palladium (Pd), samarium (Sm), oxygen (O), and nitrogen (N). Thedirection of magnetization is set by a large external in-plane fieldwithout annealing.

In other embodiments, the SEL 26 is made of multiple layers 74 formedfrom a ferromagnetic layer 80 on top of which is formed a spacer layer78, on top of which is formed a ferromagnetic layer 76. In this respect,the layers 76 and 80 are anti-ferromagnetically coupled (AFC). The layer80 has an in-plane anisotropy, as shown by the arrow 88 and the layer 76has an in-plane anisotropy, as shown by the arrow 86. In someembodiments, the layers 76 and 80 are each made of the same material asthat disclosed above for the layer 72. In some embodiments, the spacerlayer 78 is made of the same material as that disclosed for the spacerlayer 24 herein. In this embodiment, the layers 74 comprise a syntheticanti-ferromagnetic (SAF) structure having an in-plane anisotropy (ormagnetic orientation).

In some embodiments, the layer 80 is formed on top of the layer 14 andin other embodiments, the layer 74 is flipped with the layer 76 formedon top of the layer 14.

In still other embodiments, the SEL 26 is made of a FM layer 82 that isa single layer but has an out-of-plane magnetic anisotropy, as shown bythe arrow 90 and in this respect is made of material that is differentthan the layer 72.

In some embodiments, the layer 82 is made of CoPtX where X is selectedfrom one of the following materials: Cr, Ta, Mo, Zr, Nb, B, C, N, P, Ti,SiO₂, and TiO₂, and the magnetization of the layer 82 is tilted awayfrom an in-plane direction to be greater than 10 degrees.

In this embodiment, the magnetization component of the layer 82 iscontrolled and tilted toward a perpendicular direction, as shown by thearrow 90. This helps to balance the anti-parallel to parallel vs. theparallel to anti-parallel switching current offset with controlledperpendicular field on the FL 22 from perpendicular magnetizationcomponent of the layer 82.

FIG. 8 shows the element 30 to include still further embodiments of theSEL 26. Accordingly, in one embodiment, the SEL 26 is made of bilayer92, which is formed of a FM layer 100 on top of which is formed a FMlayer 98. Each of the layers 98 and 100 is made of ferromagneticmaterial and have either a different magnetic isotropy (Hk) or adifferent saturation magnetization (Ms) or a different Hk and Msrelative to one another. The direction of magnetization of the layer 100is in-plane and shown by the arrow 116 and the direction ofmagnetization of the layer 98, which is also in-plane, is shown by thearrow 114.

In yet another embodiment, the SEL 26 is made of the multi-layer 94,which is shown formed of an anti-ferromagnetic (AFM) layer 108 on top ofwhich is shown formed a FM layer 106 on top of which is shown formed aspacer layer 104, on top of which is shown formed a FM layer 102. Inthis embodiment, the AFM layer 108 is formed on top of the layer 14.Alternatively, in a bottom MTJ structure configuration 10, themulti-layer 94 is flipped such that the FM layer 102 is formed on top ofthe layer 24 and the layer 104 is formed upon it and the layer 106 isformed on top of the layer 104 and the AFM layer 108 is formed on top ofthe layer 106. In both embodiments, the layers 106 and 102 areanti-ferromagnetically coupled.

In still another embodiment, the SEL 26 is made of the bilayer 96, whichis shown made of an AFM layer 112 formed below a FM layer 110. The AFMlayer 112 is made of the same material as the layers 108 and 16, and theFM layer 110 is made of the same material as the layer 72. The layer 112helps the magnetic orientation (which is commonly referred to as“magnetization”) of the layer 110 remain in the same direction. Thedirection of the magnetic orientation of the layer 110, which isin-plane, is shown by the arrow 121.

FIG. 9 shows the element 30 to include various embodiments of the layer24. In one embodiment, the layer 24 is made of a bilayer 200, which isshown to be made of an insulator layer 210 below a metal layer 208. Inthe embodiment of FIG. 9, the layer 210 is formed on top of the SEL 26.

The layer 210 is made of any suitable insulating material, some examplesof which are magnesium oxide (MgO), silicon dioxide (SiO₂), siliconnitride (SiN), and aluminum oxide (Al₂O₃). The layer 208 is made of anysuitable metallic material, some examples of which are Ta, Ti, Ru, Pt,Cr, Cu, and Hf.

In other embodiments, the layers of the bilayer 200 are flipped, asshown by the bilayer 202 where the metal layer 214 is formed on top ofthe SEL 26 and the layer 212 is formed on top of the layer 214.

Still alternatively, the layer 24 is made of a single layer, which ismade of the same material as the layer 210. To this end, the insulatinglayer 216 is shown as another embodiment.

Yet another embodiment of the element 10 is where the layer 24 is madeof the metal layer 218, which is a single layer and made of the samematerial as the layer 208.

FIG. 10 shows the relevant portion of an STTMRAM element 120, inaccordance with another embodiment of the present invention. The element120 is shown to include the BE 12, the layer 14, the free layer 122, thelayer 20, the layer 18, the layer 16, the layer 28, a spacer layer 124,an SEL layer 126, a spacer layer 128 and an SEL 130. The layers 12, 14,122, 20, 18, 16 and 28 are shown separated from the layers 124, 126, 128and 130 by an insulating layer 132 on either side thereof. The layer122, the layer 20 and the layer 18 and the AFM layer 16 collectivelycomprise the MTJ of the element 120.

In the embodiment of FIG. 10, the layer 14 is shown formed on top of theBE 12 and the FL 122 is shown formed on top of the layer 14, the layer20 is shown formed on top of the layer 122, the layer 18 is shown formedon top of the layer 20, the layer 16 is shown formed on top of the layer18 and the layer 28 is shown formed on top of the layer 16. The SEL 126is shown formed on top of the layer 124, which is shown formed on top ofthe layer 132. Similarly, the SEL 130 is shown formed on top of thelayer 128, which is shown formed on top of the layer 132. The SEL 126 isshown to have a negative magnetic charge adjacent to the MTJ and anin-plane anisotropy in a direction consistent with the direction of thearrow 140. On the other hand, the SEL 130 has positive magnetic chargeadjacent to the MTJ and an in-plane anisotropy in a direction consistentwith the direction of the arrow 142.

As in each of the elements 10 and 30, the FL 122 has a perpendicularanisotropy, as does the layer 18. Also, the FL 122 has magnetic moments,shown by the arrows 144 that are tilted with in-plane components at thefree layer's edges, as previously discussed. This is effectively done bythe SELs 126 and 130, which in the element 120 are shown on the sides ofthe MTJ of the element 120 instead of being in or a part of the MTJ, asin each of the elements 10 and 30. Regardless, the element 120 operatesin a manner analogous to the element 10, as described above.

In some embodiments, the thickness of the layer 132 is 5-20 nano meters.There is a tradeoff for making the layer 132 too large or too small inthickness and therefore a balance to be struck. It is contemplated thatif the thickness of the layer 132 is made to be too large, themagneto-static field on the FL 122 from the SEL will undesirably decay,resulting in less switching current reduction. If the thickness is madetoo small, the process of manufacturing the element 120 will becomecumbersome or even unattainable because to make a narrow layer 132 withsuitable step coverage is extremely difficult without potential shortingof the MTJ and the SELs 126/130. For this reason, currently, themanufacturing of each of the elements 10 and 30 is contemplated to beeasier than that of the element 120.

Similar to the element 10, while the element 120 is shown to be a “topstructure”, in other embodiments, it may be a “bottom structure” withthe FL 122 formed on top of layer 18.

FIG. 11 shows a graph 170 of the behavior of the element 120 vs. that ofa prior art magnetic memory. The graph 170 has an x-axis representingthe threshold voltage, in milli Volts, and a y-axis representing theresistance, in kilo Ohms, of the MTJ of the magnetic memory whosebehavior the graph 170 captures.

In the graph 170, four curves are shown: Curve 172 shows the behavior ofa prior art magnetic memory with no SEL; Curve 174 shows the behavior ofthe curve 54 in FIG. 5 with the thickness of the SEL 26 being 3 nanometers and the Hk thereof being 5 kOe; Curve 176 shows the behavior ofthe curve 56 in FIG. 5 with the thickness of the SEL 26 being 5 nanometers and the Hk thereof being 5 kOe; and the curve 178 shows thebehavior of the element 120 with the presence of the SEL 126, whichexhibits a greater improvement over the already-improved Curves 174 and176.

Although the present invention has been described in terms of specificembodiments, it is anticipated that alterations and modificationsthereof will no doubt become apparent to those skilled in the art. It istherefore intended that the following claims be interpreted as coveringall such alterations and modification as fall within the true spirit andscope of the invention.

What is claimed is:
 1. A spin transfer torque magnetic random accessmemory (STTMRAM) element comprising: a magnetic free layer and amagnetic pinned layer in contact with a tunnel barrier layer interposedtherebetween, said magnetic free layer having a variable perpendicularmagnetic orientation, said magnetic pinned layer having an invariableperpendicular magnetic orientation; and a switching-enhancing layer(SEL) separated from said magnetic free layer by a first non-magneticspacer layer, said SEL having an invariable in-plane magneticorientation.
 2. The STTMRAM element of claim 1, wherein said magneticfree layer includes multiple ferromagnetic layers.
 3. The STTMRAMelement of claim 1, wherein said magnetic free layer comprises cobaltand iron.
 4. The STTMRAM element of claim 1, wherein said magneticpinned layer includes multiple ferromagnetic layers.
 5. The STTMRAMelement of claim 1, wherein said magnetic pinned layer comprises cobaltand iron.
 6. The STTMRAM element of claim 1, wherein said magneticpinned layer includes two ferromagnetic layers separated by a secondnon-magnetic spacer layer, said two ferromagnetic layers having oppositeperpendicular magnetization directions.
 7. The STTMRAM element of claim1, wherein said SEL includes multiple ferromagnetic layers.
 8. TheSTTMRAM element of claim 1, wherein said SEL includes a ferromagneticlayer and an antiferromagnetic layer formed adjacent thereto.
 9. TheSTTMRAM element of claim 1, wherein said SEL comprises cobalt and iron.10. The STTMRAM element of claim 1, wherein said SEL includes a firstswitching-enhancing sublayer (SES) and a second SES separated by a thirdnon-magnetic spacer layer with said first SES formed adjacent to saidfirst non-magnetic spacer layer, said first and secondswitching-enhancing sublayers having opposite in-plane magnetizationdirections.
 11. The STTMRAM element of claim 10, wherein each of saidfirst and second switching-enhancing sublayers further includes aferromagnetic layer.
 12. The STTMRAM element of claim 10, wherein saidsecond SES further includes a ferromagnetic layer and anantiferromagnetic layer formed adjacent thereto.
 13. The STTMRAM elementof claim 1, wherein said first non-magnetic spacer layer comprises ametal layer and an insulator layer.
 14. The STTMRAM element of claim 1,wherein said first non-magnetic spacer layer is made of an insulatormaterial.
 15. The STTMRAM element of claim 1, wherein said firstnon-magnetic spacer layer is made of a conductor material.
 16. TheSTTMRAM element of claim 1, wherein said first non-magnetic spacer layeris made of Ta, Ti, Ru, Ru, Pt, Cr, Cu, or Hf.
 17. The STTMRAM element ofclaim 1 further comprising a cap layer formed adjacent to said SELopposite said first non-magnetic spacer layer.
 18. The STTMRAM elementof claim 1 further comprising a seed layer formed adjacent to said SELopposite said first non-magnetic spacer layer.
 19. A spin transfertorque magnetic random access memory (STTMRAM) element comprising: amagnetic free layer and a magnetic pinned layer in contact with a tunnelbarrier layer interposed therebetween, said magnetic free layer having avariable perpendicular magnetic orientation, said magnetic pinned layerhaving an invariable perpendicular magnetic orientation; and aswitching-enhancing layer (SEL) separated from said magnetic free layerby a first non-magnetic spacer layer, said SEL having an in-planemagnetic orientation, wherein said first non-magnetic spacer layerincludes an insulator layer.
 20. The STTMRAM element of claim 19,wherein said magnetic free layer includes multiple ferromagnetic layers.21. The STTMRAM element of claim 19, wherein said magnetic pinned layerincludes multiple ferromagnetic layers.
 22. The STTMRAM element of claim19, wherein said magnetic pinned layer comprises cobalt and iron.
 23. Aspin transfer torque magnetic random access memory (STTMRAM) elementcomprising: a magnetic free layer and a magnetic pinned layer in contactwith a tunnel barrier layer interposed therebetween, said magnetic freelayer having a variable perpendicular magnetic orientation, saidmagnetic pinned layer having an invariable perpendicular magneticorientation; and a switching-enhancing layer (SEL) separated from saidmagnetic free layer by a first non-magnetic spacer layer, said SELhaving an in-plane magnetic orientation, wherein said magnetic pinnedlayer includes two ferromagnetic layers separated by a secondnon-magnetic spacer layer, said two ferromagnetic layers having oppositeperpendicular magnetization directions.
 24. The STTMRAM element of claim19, wherein said SEL includes multiple ferromagnetic layers.
 25. TheSTTMRAM element of claim 19, wherein said SEL comprises cobalt and iron.26. The STTMRAM element of claim 19, wherein said first non-magneticspacer layer is made of a conductor material.
 27. The STTMRAM element ofclaim 19, wherein said first non-magnetic spacer layer is made of Ta,Ti, Ru, Pt, Cr, Cu, or Hf.
 28. A spin transfer torque magnetic randomaccess memory (STTMRAM) element comprising: a magnetic free layer and amagnetic pinned layer in contact with a tunnel barrier layer interposedtherebetween, said magnetic free layer having a variable perpendicularmagnetic orientation, said magnetic pinned layer having an invariableperpendicular magnetic orientation; and a switching-enhancing layer(SEL) separated from said magnetic free layer by a first non-magneticspacer layer, said SEL having an in-plane magnetic orientation, whereinsaid SEL includes a first switching-enhancing sublayer (SES) and asecond SES separated by a third non-magnetic spacer layer with saidfirst SES formed adjacent to said first non-magnetic spacer layer, saidfirst and second switching-enhancing sublayers having opposite in-planemagnetization directions.
 29. The STTMRAM element of claim 28, whereineach of said first and second switching-enhancing sublayers furtherincludes a ferromagnetic layer.